1. Field of the Invention
The invention relates to thickening vinyl copolymers, particularly hydrophobically modified alkali-swellable or alkali-soluble emulsion polymers.
2. The Related Art
Rheology modifiers are used as thickeners and structurants in a variety of consumer and industrial products. They affect product performance, aesthetics, application and suspension, and delivery of active chemical agents. Rheology modifiers are generally classed in several categories dependent on the mechanism by which they thicken.
Hydrodynamic thickeners work by utilizing acid groups in their structure that when neutralized form anionic charges. These repel each other causing the polymer chains to expand and entangle. Thickening and suspending effects of the neutralized polymers are due to increased physical packing of the molecules. These materials are also known as “space filling” or “volume exclusion”. Both viscosity and yield point increase with concentration. The alkali swellable emulsions (ASE) and carbomers fall within this category.
Associative thickeners operate by a twin mechanism. They utilize the aforementioned hydrodynamic thickening method. Secondly, they utilize the association of hydrophobic groups on the polymer backbone with other hydrophobic species. The latter can be other hydrophobic polymer groups, oils, particles and the like. Association creates hydrophobic regions distributed throughout the polymer chain network. This also renders the polymers as effective solubilizing agents. The hydrophobically modified alkali swellable emulsions (HASE) fall into this category.
HASE/ASE polymers are produced by oil-in-water emulsion polymerization. Most consist of a lightly crosslinked backbone of ethyl acrylate and methacrylic acid.
U.S. Pat. No. 4,529,773 (Witiak et al.) reports alkali-soluble emulsion polymers activated by neutralization to a pH above 6.5, and subsequently acidified in the presence of a surfactant. These are described as useful thickeners in acidified containing compositions. The polymers are best formed from a 3-component monomer system of methacrylic or acrylic acid, methacrylic or acrylic acid ester of a C8-C30 alkyl or hydrocarbyl monoether of polyethylene glycol, and a C1-C4 alkyl acrylate or methacrylate.
U.S. Pat. Nos. 7,649,047 B2 and 7,288,616, both to Tamareselvy et al., disclose multi-purpose alkali-swellable and alkali-soluble associative polymers. They are formed from polymerizing a monomer mixture of at least one acidic vinyl monomer, at least one nonionic vinyl monomer, a first associative monomer having a first hydrophobic end group, a second associative monomer having a second hydrophobic end group, and a crosslinking or chain transfer agent. These patents describe the HASE type chemistry. A commercial product based on this chemistry is the Lubrizol Corp. supplied Aqua SF-1®.
WO 2010/026097 A1 (Graham et al.) describes rheology modifiers for use in home and personal care compositions. These modifiers are formed from four monomers. They include an amino-substituted vinyl monomer, a hydrophobic nonionic vinyl monomer (such as a C1-C30 alkyl ester of acrylic or methacrylic acid), an associative-like monomer (with a polyoxyalkylene unit end-capped with a hydrophobic group), and a further associative-like vinyl monomer.
Although the aforementioned disclosures and their commercial embodiments provide rheology modifying solutions, there still is a need for improvements in thickening profile and suspension clarity.